Passive check valves are known. There are numerous types of passive check valves, including flap-type valves, ball valves, and disc valves. Known disc check valves are typically biased closed via a spring or other mechanism. Liquid that flows against the disc during normal operation opens the valve, allowing liquid to flow through the valve in a forward direction. If the liquid reverses flow so that there is no longer any flow in the forward direction, the disc slams closed because the spring biases the disc into a closed position. This prevents the valve from flowing in an unintended direction.
Passive check valves are commonly used in piping systems to prevent backflow from damaging systems that are upstream of the valve. For example, check valves can be used in a piping system that includes a pump that is positioned upstream of the check valve. Should flow reverse, it is important that the reversing flow not be permitted to engage the pump. Reverse flow into the turbine of a pump could cause serious damage to the pump.
Passive check valves are also utilized in nuclear power plants. In nuclear power plants, a flow path is coupled to the nuclear-reactor that will allow cooling water to enter a containment center in the event of an accident. Flow is permitted from the cooling reservoir into the containment center in order to cool the reactor. However, reverse flow is highly undesirable since it will potentially allow hot, radioactive material to flow outside the containment center. Passive check valves are utilized in systems such as this in order to prevent the reverse flow of fluid through the check valve. The USA Nuclear Regulatory Commission requires maintaining plant safety. Those requirements include, among other things, plant operating procedures that require that check valves and other safety-related equipment be tested periodically to verify proper operation. This results in increased safety and reliability in the design of nuclear power plants.
Check valves in nuclear plant systems may often sit idle for years. It is important that they be tested to confirm that they will work in the event of an accident.